AlphaGo (roughly) may try many things to win at go, varieties of joseki or whatever.

I'm not sure that AlphaGo has any conception of what a joseki is supposed to be.

Moves have a certain 'go-winningness' to them (and camps full of losers forfeiting over and over has a higher go-winningness' than any), and it prefers higher. Saying that 'go-winning' isn't 'go-winning' doesn't mean anything.

Are the moves that AlphaGo played at the end of game 4 really about 'go-winningness' in the sense of what it's programmers intended 'go-winningness' to mean?

I don't think it's clear that every neural net can propagate goals through itself perfectly.